Staples have a variety of uses. For example, surgeons use thin wire staples to join the cut ends of hollow organs or ducts (anastomosis) and to achieve hemostasis. Thin wire staples are made by deforming a length of thin wire with uniform cross section and material properties to a U-shape. FIG. 1 shows a common prior art thin wire staple 100, including a crown 101 and two legs 102. The staple shown in FIG. 1 has uniform cross section and material properties, except as these may be altered in the region where the staple legs join the crown during deformation of the wire to the U-shape. Surgical staples are made of materials inert to attack by body fluids, e.g., stainless steels.
When a staple is installed, its legs are pushed into the material being stapled. During installation, some staples are deformed, i.e., bent past their elastic limit to achieve a permanent change in shape.
FIG. 2 shows the staple of FIG. 1 deformed to a B-shape during installation due to its legs having being forced against an anvil with channels to direct the legs as they bend and deform. This anvil is located on the side of the material being stapled that is opposite to the side into which staple insertion is made. The deformation of the staple of FIG. 1 occurs in its leg region at and near the legs' juncture with the crown, since this is where the maximum bending stress develops.
FIG. 2 shows that the separation of different locations on the legs 102 from the crown 101 varies for a B-shaped staple. Thus, when B-shaped staples are used in surgery, tissues located between different regions of the legs and the crown undergo different compressions, and tissue compression varies in the vicinity of the gap between leg ends when these ends are not in close proximity.
To achieve hemostasis using staples, the tissue compressed least by the staples must still be compressed sufficiently for the hemostasis despite the possibility that the tissue compressed most may be perforated or damaged due to excessive compression or distortion. Necrosis, additional scar tissue formation and longer healing times can result from excessive compression or distortion. Shrinkage of scar tissue over time can lead to adverse results, and thus it is important to avoid forming more scar tissue than necessary.
If the curvature of the staple legs where they join the crown is large, i.e., if the staple has a small radius at the junctures of the legs and the crown, then the separation between the legs and the crown will be small, and tissue may undergo excessive compression. If the curvature is small, i.e., if the staple has a large radius at the junctures of the legs and the crown, then tissue distortion may be excessive in the vicinity of the junctures.
It is an object of the present invention to provide a staple which achieves uniform compression of stapled material.
It is also an object of the present invention to provide a surgical staple which minimizes scar tissue formation.
It is a further object of the present invention to provide a staple which minimizes distortion of the material stapled.
It is an additional object of the present invention to provide a surgical staple which minimizes healing time.
It is a further object of the present invention to provide a staple which minimizes damage of material stapled.